This application is based on and claims priority to Japanese Patent Application No. 2000-215162, filed Jul. 14, 2001, the entire contents of which is hereby expressly incorporated by reference.
1. Field of the Invention
The present invention relates generally to an air induction system for an engine, and more particularly to an improved induction system for an engine that has an auxiliary air intake device.
2. Description of Related Art
An internal combustion engine typically comprises an air induction system with which air is introduced into a combustion chamber of the engine. Typically, the induction system includes an air intake conduit, a plenum chamber unit disposed upstream of the air intake conduit and a throttle valve. The plenum chamber unit is used to reduce pulsation in the airflow to the combustion chamber and/or to reduces noise in the intake system. The throttle valve measures an amount of the air (i.e., controls the airflow rate) and is operable by the operator through an appropriate throttle linkage. The induction system thus can supply a desired amount of air to the combustion chamber in response to a throttle opening degree corresponding to operator demand.
In most engine technologies, the engine maintains a certain preset engine speed although substantially no engine load is being applied; this is an idle condition. Typically, the throttle valve is held in an almost closed position under the idle condition. In some engine configurations, an auxiliary intake conduit is provided to bypass the throttle valve so that a certain preset amount of air can be supplied to the combustion chamber even through the throttle valve is substantially closed under the idle condition. For example, U.S. Pat. No. 6,015,319 discloses an improved arrangement of an air induction system that includes such a bypass intake conduit.
Although the idle air is delivered to the combustion chamber through the auxiliary intake conduit, the throttle valve desirably is slightly opened to allow a light air flow through the primary intake conduit to prevent sticking of the throttle valve when higher engine speed operation is desired. Under these circumstances, a problem can arise; the idle speed can exceed a desired objective idle speed or the engine can stall. These two conditions result because the amount of idle air that the engine requires is extremely small because only a low rate of airflow is necessary to maintain a desired objective idle speed. The low rate of airflow is quite sensitive and is likely to be out of tune by external forces such as a negative pressure exerted upon the air. The negative pressure can be produced by the light air flow through the primary intake conduit.
A need therefore exists for an improved air induction system for an engine that can provide an accurate amount of idle air to a combustion chamber thereof.
In some configurations, outboard motors can employ an air induction system that includes an auxiliary intake conduit. Outboard motors also often have a certain decibel of noise associated with their operation. Because the outboard motor typically is used adjacent to the operator (i.e., mounted to the transom of the watercraft), intake noise preferably is isolated from the operator as much as possible.
Another need thus exists for an improved engine for an outboard motor that can isolate the intake noise from the operator as much as possible when the outboard motor is in use.
In accordance with one aspect of the present invention, an internal combustion engine comprises an engine body and an air induction system. The engine body comprises a cylinder block defining a cylinder bore in which a piston reciprocates. A cylinder head member closes an end of the cylinder bore to define a combustion chamber together with the cylinder bore and the piston. The air induction system is arranged to introduce air into the combustion chamber. The induction system includes a first intake conduit through which the air flows to the combustion chamber. A first plenum chamber unit is disposed upstream the first intake conduit. A control mechanism is arranged to control an amount of the air flowing through the first intake conduit. The induction system includes a second intake conduit through which the air flows to the combustion chamber. A second plenum chamber unit is disposed upstream the second intake conduit. The second intake conduit is coupled with the first intake conduit downstream the control mechanism.
In accordance with another aspect of the present invention, an internal combustion engine comprises an engine body. A moveable member is moveable relative to the engine body. The engine body and the moveable member together define a combustion chamber. An air induction system is arranged to introduce air into the combustion chamber. The induction system includes a primary intake conduit through which the air flows to the combustion chamber. A first voluminous unit is disposed upstream the primary intake conduit. A throttle valve is arranged to control an amount of the air flowing through the primary intake conduit. The throttle valve generally allows the majority of the air to flow through the primary intake conduit at engine speed above idle. The induction system includes an auxiliary intake conduit through which at least the air at idle speed flows to the combustion chamber. A second voluminous unit disposed upstream the auxiliary intake conduit. The auxiliary intake conduit is coupled with the primary intake conduit downstream the throttle valve.
In accordance with a further aspect of the present invention, an internal combustion engine comprises an engine body. A moveable member is moveable relative to the engine body. The engine body and the moveable member together define a combustion chamber. An air induction system is arranged to introduce air into the combustion chamber. The induction system includes an intake conduit through which the air flows. A first member is provided. A second member is provided. The second member, together with the first member, defines a plenum chamber disposed upstream the intake conduit. Both the first and second members are mounted on the engine body. The first and second members are coupled with one another to form a gap therebetween through which the air enters the plenum chamber.
In accordance with a still further aspect of the present invention, an outboard motor comprises a drive unit. A bracket assembly is adapted to be mounted on an associated watercraft to support the drive unit. The drive unit includes an internal combustion engine. The engine comprises an engine body. A moveable member is moveable relative to the engine body. The engine body and the moveable member together define a combustion chamber. An air induction system is arranged to introduce air into the combustion chamber. The induction system includes a first intake conduit through which the air flows to the combustion chamber. A first plenum chamber unit is disposed upstream the first intake conduit. A control mechanism is configured to control an amount of the air flowing through the first intake conduit. The induction system includes a second intake conduit through which the air flows to the combustion chamber. A second plenum chamber unit is disposed upstream the second intake conduit. The second intake conduit is coupled with the first intake conduit downstream the control mechanism. The second plenum chamber unit is disposed opposite to the bracket assembly relative to the engine body.